The hydraulic control system has been used for many years in the agricultural and industrial field to actuate various components in vehicles used for these purposes. These components, generally referred to as loads, may be a plows, discs, backhoes, augers and many other types of devices. The hydraulic systems generally comprise a pump (usually driven by the prime mover for the vehicle) that pressurizes hydraulic fluid for selective delivery to actuators to manipulate a load. The typical actuator has a piston within a chamber attached to an output shaft. Hydraulic fluid is selectively directed to either face of the piston in order to displace the actuating rod. This enables a force to be applied to the load that is far greater than any operator could do through mechanical linkages.
Early systems of this type used a manual actuation of the valve controlling hydraulic fluid to either side of the actuator piston. As implements and equipment have become more complex and complicated the manual actuation of the valve has been replaced by electro-hydraulic systems.
Many electro-hydraulic systems supply pressurized fluid to at least one, and preferably two faces of a control valve that directs pressurized fluid to the actuator. Solenoid operated valves direct control fluid from an appropriate source, which in a typical case is the same as the actuating fluid. The solenoid valves are controlled from an appropriate controller so that the valve elements may be dispersed throughout the vehicle and do not have to be adjacent the operator for manual actuation. The use of electrical signals to control this function also enables additional control functions and sophistication in terms of safety overrides and other advanced system requirements.
One of the problems, however, with electro-hydraulic valves is that with agricultural and industrial equipment the vehicle frequently is stored outside and is exposed to whatever ambient temperature is adjacent the vehicle. The hydraulic fluid is a viscosity dependent liquid that has a significant increase in viscosity for low ambient temperatures. As such, initial startup of systems of this type experience sluggish response to control inputs owing to the fact that the passages for the control of the main valve are relatively small, thus causing a delay in delivery of fluid to the end of the valve element. There have been a number of proposals that establish secondary and discrete circuits to achieve warm-up of the system by pressurizing and throttling the pressurized fluid to a drain. However, these add unnecessary expense and complication to the system.
Accordingly, what is needed in the art is a simplified system for increasing the temperature of hydraulic fluid for systems of this type.